Processing waste rubber by steam pyrolysis

ABSTRACT

The invention relates to the technology of reprocessing industrial and domestic waste. The problem addressed is reducing energy consumption and the quantity of toxic waste which enters the environment when rubber waste is reprocessed. This problem is solved by the use of superheated steam for the pyrolysis of the waste material. Superheated steam, amounting to between 18 and 110 percent of the mass of the rubber waste, is used as the heat carrier. The gaseous products of pyrolysis are condensed together with the steam, and the condensate thus obtained is mixed with the solid residue which has first undergone preliminary grinding to produce particles of between 0.001 and 0.210 mm in size. The quantity of solid residue in the mixture is set at between 23 and 55.8 percent of the total mass of the mixture. This process results in the production of a liquid fuel with improved environmental characteristics.

FIELD OF THE INVENTION

This invention relates to the technology of processing industrial anddomestic waste. It can be used in the rubber industry and in thefuel-power industry for use of waste rubber as a fuel.

BACKGROUND OF THE INVENTION

There exists a method of processing waste to obtain liquid and gaseousfuel by means of pyrolysis and decomposition of the products ofpyrolysis into solid, liquid and gaseous phases. The solid phase isrestored by water vapor with the formation of carbon monoxide andhydrogen; the gaseous phase is partially removed for maintaining theprocess of pyrolysis, and the remaining part is mixed with condensed andisolated from water resin (see Alexeyev G. M., Petrov V. N., ShpilfogelP. V. Industrial methods of sanitary cleaning of cities.-L. Stroyizdat,1983, p. 14-15).

Disadvantages, associated with this method are the following: high powerconsumption as a result of high temperatures (up to 1500° C.) existingin the reactor; technical difficulties, arising in the process ofisolation of resin from water; and great outflow of toxic substancesinto the surroundings.

The most similar to the invention is a method of processing wasterubber, taken as prototype, according to which pyrolysis of waste iscarried out in the medium of heat carrier-arenaceous quartz; solid phaseis isolated, liquid and gaseous phases are separated by condensation andthe gaseous phase is removed and burnt for maintaining the process ofpyrolysis (see Palgunov P. P, Sumarockov M. V. Utilization of IndustrialWaste.-M. Stroyizdat, 1990, p. 165-166).

The disadvantages of this method are the following: high powerconsumption (specific heat consumption is 12.5 megajoules/kg); hightemperature of the process (T=500°-700° C.) that makes it necessary touse special heat-resisting steels in pyrolysis plants; a large amount ofcombustion products introduced into the atmosphere (outflow of productsof combustion is 2.5 kg/kg of the waste subjected to pyrolysis); greatdanger of explosion of gases of pyrolysis due to a large amount ofhydrogen in them (hydrogen content in pyrolysis gas is 48-52%).

SUMMARY OF THE INVENTION

This invention is aimed at reducing power consumption and lowering theamount of harmful outflow into the surroundings during the process ofobtaining fuel from waste rubber.

The aim is achieved by this method of processing waste rubber, includingpyrolysis of waste in the medium of a heat carrier, isolation of solidphase, separation of liquid and gaseous phases by condensation andremoving and burning of gaseous phase for maintaining the process ofpyrolysis. Superheated water vapor is used as the heat carrier and thequantity of superheated water vapor is 18-110% of the mass of waste. Thesolid phase after separation is ground to particles of 0.001-0.210 mm,liquid phase is separated together with vapor and mixed with 23.0-55.8%of ground solid phase to obtain liquid fuel.

It is known (see Alexeyev G. M., Petrov V. N., Shpilfogel P. V.Industrial Methods of Sanitary Cleaning of Cities.-L. Stroyizdat, 1983,p.44-45), that the process of pyrolysis of waste rubber begins at T=400°C. and ends at T=500° C., therefore the temperature in the reactor mustrange from 400° to 500° C. For keeping such a temperature level in thereactor a certain amount of superheated water vapor is needed.

As waste rubber is heated by the warmth of the superheated water vapor,and the temperature of the superheated water vapor is in fact 100°-1600°C., then the maximum quantity of the superheated water vapor necessaryfor heating the waste to T=400°-500° C is 18-110% of the mass of thewaste subject to pyrolysis.

If less than 18 mass percent of superheated water vapor is used, wasterubber will not be heated to T=400° C. (it will be heated to a lowertemperature) and the process of pyrolysis will not occur.

If more than 110 mass percent of superheated water vapor is used wasterubber will be heated to more than 500° C. which will cause a decreasein the useful products of pyrolysis, increase the consumption of theheat carrier and increase the harmful gaseous outflow into thesurroundings i.e. breaking the process of pyrolysis.

The degree of grinding of the solid remainder is based on the following:the smaller the diameter of the particles, the more homogeneous andstable. There may be the mixture of particles. However, the lower limitof the degree of grinding is determined by technical potentialities andis equal to 0.001 mm. The upper limit of grinding is determined by thestability limit of the mixture and is 0.210 mm in our case.

If particles with a diameter of more than 0.210 mm are used the mixtureof particles condensate (liquid phase) will lose liquid mass stability,i.e. the particles will precipitate.

For preventing harmful outflow into the surroundings (pouring out ofcondensate), it is necessary to mix the whole condensate with solidphase. Thus, the content of the solid remainder in the mixture will be23.0-55.8 mass percent.

Making a mixture with the content of solid remainder less than 23.0 masspercent results in the need to pour out a part of condensate into thesurroundings, that results in pollution and loss of some useful productsof pyrolysis of waste.

Making mixture with the content of solid reminder more than 55.8 masspercent, cause a part of the solid remainder to precipitate and as aresult liquid mass stability of the mixture will be broken, hence thehomogeneity of liquid fuel, i.e. the quality of the fuel (density,viscosity heat of combustion) will get much worse.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of the device for realization of the method ofprocessing waste rubber.

DETAILED DESCRIPTION OF THE INVENTION

The device has reactor 1 with lock hatch 2 for waste rubber 3. Steamgenerator 4 through tap 5 and consumption indicator 6 is connected tothe reactor. Vapor pressure in the reactor is controlled by theindication of the manometer 7. The temperature in the reactor iscontrolled by the indication of thermometer 8.

Gases from reactor 1 go to condenser 9. Incondensable gases through tap10 and consumption indicator 11 go to combustion chamber of steamgenerator 4. Condensed water vapor and the products of pyrolysis go fromcondenser 9 to storage chamber 12.

Screw 13, rotated by engine 14, transports solid remainder of pyrolysisof waste rubber to mill 15. After grinding solid remainder istransported to mixer 18 through weight doser 16 with lock 17. Throughconsumption indicator 19 and tap 20 condensate from storage chamber 12goes to mixer 18.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

According to the present invention waste rubber is processed as follows.

Waste rubber 3, for example rubber tires, are transported into reactor 1through lock hatch 2. Simultaneously, water vapor having a temperaturefrom 400° to 1600° C. goes from steam generator 4 to the reactor throughtap 5 and consumption indicator 6. Vapor pressure in reactor 1 iscontrolled by indication of manometer 7. Superheated water vapor, goingto the reactor, heats waste rubber up to the temperature at whichpyrolysis of waste rubber occurs, resulting in isolation of solid andliquid constituents.

The temperature in the reactor is controlled by indication ofthermometer 8.

At temperatures from 400° to 500° C. thermal decomposition of wasterubber occurs. The gases of decomposition together with water vapor goto condenser 9, where vapor and a portion of gaseous products ofpyrolysis condense.

Incondensable gases through tap 10 and consumption indicator 11 aretransported for burning to combustion chamber of steam generator 4.

Condensed water vapor and the products of pyrolysis go from condenser 9to storage chamber 12.

Solid remainder of pyrolysis of waste rubber is transported by screw 13,rotated by engine 14 to mill 15 and is ground to particles withdiameters of 0.001-0.210 mm. After grinding, the solid remainder istransported to mixer 18 through weight doser 16 with lock 17.

Simultaneously, condensate from storage chamber 12 is transported tomixer 18 through consumption indicator 19 and tap 20, the quantity ofsolid remainder in the mixture being 23-55.8% of the mass of themixture.

Condensate and solid remainder are mixed in the mixer to a homogeneousdispersion of solid particles in condensate. The homogeneous mixture ispoured out into containers.

EXAMPLE 1

1000 kilograms of waste rubber 3 is loaded into reactor 1 through lockhatch 2. Simultaneously, superheated water vapor having T=400° C. istransported from steam generator 4 to reactor 1 through tap 5 andconsumption indicator 6. Vapor pressure in reactor 1 is controlled bymanometer 7 (the pressure kept is 10 ⁵ Pascal). The amount of watervapor to be transported to reactor 1 in order to heat 1000 kg of wasterubber to the temperature of the beginning of pyrolysis is 1100 kg.

The temperature in the reactor is controlled by indication ofthermometer 8. When waste rubber is heated up to 400° C., the process ofthermal decomposition of waste with isolation of gaseous productsbegins. Gaseous products of pyrolysis in mixture with water vaporcondense in condenser 9, which is cooled by water.

Let the amount of gaseous products, isolated during decomposition ofwaste rubber, be 40 mass percent, from which 25% condense and 15% areincondensable gases.

Thus, 1100 kg of water vapor and 250 kg of the products of pyrolysiscondense, i.e. 1100 kg+250 kg=1350 kg of condensate are formed.Incondensable gases (150 kg) go through tap 1 and consumption indicator11 are transported for burning to combustion chamber of steam generator4. Let specific heat of combustion of gases be 30 megajoules/kg. Itmakes it possible to get 4500 megajoules after combustion of 150 kg ofvapor. To obtain 1100 kg of vapor, it is necessary to use 3733megajoules. Let the losses during formation of superheated vapor be 15%,then the amount of heat needed is 4293.64 megajoules.

Thus, heat from combustion of 150 kg of gas (4500 megajoules) issufficient for obtaining the required amount of superheated water vapor.Condensate from condenser 9 is poured out into storage chamber 12.

After thermal decomposition waste rubber 3, the solid remainder istransported by screw 13, rotated by engine 14 to mill 15 for grinding.Solid remainder is reduced to particles with diameters of 0.001-0.210 mmdue to grinding and sifting through a sieve with openings 0.210 mm.After grinding solid remainder goes to weight doser 16 where it isweighed. In our case the weight of solid remainder is 600 kg. Afterweighing the remainder is transported to mixer 18 through lock 17.Condensate from storage chamber 12 is transported to mixer throughconsumption indicator 19 and tap 20. In our case the amount ofcondensate is 1350 kg. Liquid and solid phases are mixed in the mixer tohomogeneous mass. In this case quantitative content of solid remainderis 30.7%.

Ready mixture is poured out into containers.

EXAMPLE 2

300 kg of waste rubber are loaded into reactor 1 through lock hatch 2.Simultaneously, superheated water vapor having T=1600° C. is transportedfrom steam generator 4 to reactor 1 through tap 5 and consumptionindicator 6. Vapor pressure in reactor 1 is controlled by indication ofmanometer 7.

The amount of water vapor to be transported to reactor 1 in order toheat 300 kg of waste to 500° C. is 55 kg, that is 18% of the mass ofwaste, subject to pyrolysis.

The temperature in reactor 1 is controlled by indication of thermometer8.

Gaseous products of pyrolysis in mixture with water vapor condense incondenser 9. Let the amount of gaseous products, isolated duringdecomposition of this waste rubber be 37 mass percent from which 32%condense and 5% are incondensable gases. Thus, 96 kg of the products ofpyrolysis and 55 kg of water vapor condense, making 151 kg ofcondensate.

Incondensable gases (15 kg) through tap 10 and consumption indicator 11are transported for burning to combustion chamber of steam generator 4.If specific heat of combustion is 30 megajoules/kg, combustion of 15 kgof gas will give the following amount of heat: 30 megajoules ×15 kg=450megajoules. At the same time for obtaining 55 kg of vapor with T=1600°C. it is necessary to use 310 megajoules taking into account 15% of heatloss, the amount of necessary heat will be 356.5 megajoules, i.e. theheat from combustion of 15 kg of gas (450 megajoules) is sufficient forobtaining superheated water vapor.

Condensate from condenser 9 is poured out into storage chamber 12.

After thermal decomposition of waste rubber 3 the solid remainder istransported by screw 13, rotated by engine 14, to mill 15 for grinding.The solid remainder is reduced to particles with diameters ranging from0.001 to 0.210 mm. After grinding the solid remainder goes to weightdoser 16 where it is weighed. In our case the weight of solid remainderis 189 kg. After weighing the remainder is transported to mixer 18through lock 17.

Condensate from storage chamber 12 is transported to mixer throughconsumption indicator 19 and tap 20. In our case the amount ofcondensate is: 96 kg+55 kg=151 kg. Liquid and solid phases are mixed inmixer to homogeneous mass. In this case quantitative content of solidremainder in the mixture is 55.6%.

Ready mixture is poured out into containers.

APPLICATION IN INDUSTRY

Thus, obtaining liquid fuel from waste rubber according to the presentmethod makes it possible (in comparison with the best known analoguesand prototype) to reduce power consumption and lower the amount ofharmful outflow into the surroundings because the gases formed are usedas power supply of the process of obtaining fuel, hence extra powersources are not needed. Lowering the temperature of process from500°-700° C. to 400°-500° C. also makes it possible to save energy.

Besides, the composition of the fuel obtained provides high ecology notonly in the process of obtaining fuel, but during combustion of liquidfuel obtained according to this method, reduction of 20-50% of harmfuloutflow of nitric oxides into surroundings is reached due to thebalanced composition and presence of optimum quantity of water in thefuel.

What is claimed is:
 1. A method for processing waste rubbercomprising:a) pyrolyzing waste rubber at a temperature of 400° C. to500° C. using superheated water vapor to obtain solids, gases ofdecomposition and water vapor, wherein the amount of superheated watervapor is 18-110% of the mass of waste rubber to be pyrolyzed; b)separating the solids of step a), and grinding the solids to particlesof 0.001 mm to 0.210 mm; c) condensing the gases of decomposition andwater vapor of step a) to obtain liquid, and incondensable gas; d)burning the incondensable gas to maintain the pyrolysis of step a); ande) mixing the liquid formed in step c) with 23.0 to 55.8 mass percent ofthe ground solid phase of step b).